Hydraulic control system

ABSTRACT

The drawings illustrate an improved, simplified hydraulic control system for use with a continuously variable drive ratio transmission, the system being responsive to engine governor pressure and engine vacuum to provide constant speed or partthrottle operation and full-throttle operation, the latter producing results comparable to the speed rise curve obtained in a transmission embodying a hydrokinetic torque converter.

United States Patent [191 Shellman et al.

[ HYDRAULIC CONTROL SYSTEM [75] Inventors: Carl E. Shellman, Livonia;Nils P.

Week, Allen Park, both of Mich.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Oct..2, 1972 [21] Appl. No.: 294,085

933,643 Great Britain 74/860 LO & INT RELIEF VALVE VALVE RNDSL RATIODISCRIMINATOR CHECK VALVE CONSTANT SPEED VALV E GOVERNOR OFF VALV E [45]Feb.5, 1974 Primary ExaminerArthur I. McKeon Attorney, Agent, orFirm-John P. Moran 57 ABSTRACT The drawings illustrate an improved,simplified hydraulic control system for use with a continuously variabledrive ratio transmission, the system being responsive to engine governorpressure and engine vacuum to provide constant speed or part-throttleoperation and full-throttle operation, the latter producing resultscomparable to the speed rise curve obtained in a transmission embodyinga hydrokinetic torque converter. v

7 Claims, 2 Drawing igures STROKE CY LINDERS SUMP ENGINE GOVERNORASSEMBLY MODULA RATIO LIMIT VALVE Patented Feb; 5, 1974 1 HYDRAULICCONTROL SYSTEM This invention relates generally to hydrauliccontinuously systems and, more particularly, to hydraulic controlsystems for use with a device having continuously variable ratiopositions.

It is desirable for use with a constiuously variable drive ratioposition device, such as a toric or traction-drive roller and race-typetransmission, or the swash plate-type pump of a hydrostatictransmission, to have a hydraulic control system whose controlparameters are engine speed and engine vacuum, with provisions forcontrolling the'rate of engine acceleration vs. MPH. to minimizeobjectionable engine noise while providing maximum tractive drivecomparable in operation to the effect of a hydrokinetic torqueconverter.

Accordingly, an object of the invention is to provide an improvedhydraulic control system adapted to operate in response to hydraulicsignals indicative of engine speed and engine vacuum. 7

Another object of the invention is to providean improved hydrauliccontrol system embodying engine governor pressure and engine vacuum toprovide two modes of operation, i.e., constant speed and full throttleoperation.

Still another object of the invention is to provide an improvedhydraulic control systemwherein: (1) during part-throttle operation, foreach throttle opening there is a corresponding speed and vacuumcondition in response. to which the control system varies the ratioposition of the controlled device; and (2) for full-throttle operationwhere the speed called for exceeds a predetermined'value, say, 2,400rpm, the control system provides a stall speed of 2,400 rpm, with enginespeed thereabove being caused to follow a curve whichis similar to thespeed rise curve of a hydrokinetic torque converter in order to avoidobjectionable engine noise. A further object of the invention is toprovide an improved hydraulic'control system wherein a first valvearrangement provides fluid pressure indicative of constant speed to theratio control device by establishingv a pressure corresponding to eachspeed and vacuum condition, and asecond valve arrangement is responsiveto engine speed only to overrule the first valve arrangementunderfull-throttle operation above a prede termined engine speed, say, 2,400rpm.

These and other objects and advantages of the invention will be apparentwhen reference ismade to the fol lowing description and accompanyingdrawings, wherein:

FIG. 1 is a schematic illustration of a hydraulic control systemembodying the invention; and

FIG. 2 is a graphic representation of operating characteristics of theinvention.

Referring now, to the drawings in greater detail, the Figure illustratesa hydraulic control system 10 including any device having continuouslyvariable ratio posivalve 22; a manual valve 24; a ratio limit valve 26;a governor cut-off valve 28; a constant speed valve 30; a ratiodiscriminator check valve 32; and low and intermediate relief valves 34and 36, respectively.

Insofar as the hydraulic circuit is concerned, the pump embodied in thedevice 12 provides a predetermined line pressure of, say, 100 psi, tolines 38, 40, and 42 leading, respectively, to the governor assembly 14,the servo control valve 22, and to a line 44 which communicates linepressure from the line 42 to the vacuum modulator assembly 16, theconstant speed valve 30, and a branchline 46 leading to the governorcut-off valve 28. Lines 48 and 50 communicate between the servo controlvalve 22 and the forward and reverse stroke cylinders 18 and 20,respectively.

A line 52 communicates governor pressure between the governor assembly14 and a line 54 which, in turn, communicates with the constant speedvalve 30, the ratio limit valve 26, and a branchline 56 leading to thegovernor cut-off valve 28.

A line 58 and an interconnecting branchline 60 communicate modulatedpressure from the vacuum modulator assembly 16 to the constant speedvalve 30. A line 62 communicates pressure indicative of constant speedbetween the constant speed valve 30 and the ratio discriminator checkvalve 32; and lines 64 and 66 communicate ratio pressure from the ratiodiscriminator check valve 32 to the manual valve 24 and a midportion ofthe ratio limit valve 26, respectively. A branchline 68 connects betweenthe line 66 and an end portion of the ratio limit valve 26. A line 70communicates limit feed pressure between the ratio limit valve 26 andthe governor cut-off valve 28.

A central exhaust line 72 communicates between the governor cut-offvalve 28 and the servo control valve 22, with exhaust branchlines 74 and76 leading from the exhaust line 72 to the ratio limit valve 26, anexhaust branchline 78 leading from the exhaust line 72 to anotherportion of the servo control valve-22, an ex haust branchline 80 leadingfrom the line 72 to an end portion of the vacuum modulator assembly 16,and another exhaust branchline 82 leading from the exhaust line 72 tothe manual valve 24. Further exhaust branchlines 84 and 86 lead from theexhaust branchline 82 to an end portion of the manual valve 24 and tothe constant speed valve 30; and still another exhaust branchline 88leads from the exhaust branchline 80 to a midportion of the vacuummodulator assembly 16. An additional exhaust line 90 leads from theservo control valve 22, where it communicates with the central exhaustline 72, to a sump 92.

Lines 94 and 96 communicate respective forward and reverse ratiopressure between the manual valve 24 and the servo control valve 22,while lines 98 and 100 communicate the forward ratio pressure betweenthe manual valve 24 and the low and intermediate relief valves 34 and36, respectively. 7

VACUUM MODULATOR'ASSEMBLY The assembly 16 includes a housing 102 havingan end flange 103, a central bore 104 which is divided into chambers106, 108, and 112 by lands 113, 114, 116 and 118 formed on a spool valve120 slidably mounted in the bore 104. The end flange 103 is counterboredto form a chamber 121 with the adjacent face of the land 1l3.'Anend-cover 122, including an inlet fitting 123, is secured to the face ofthe flange 103 by bolts 124 so as to secure the outer edge ofa diaphragm125 therebetween, the latter separating chamber 121 from a chamber 126within the cover 122. The end face 127 of the valve 120 abuts against asolid member 128 secured to the diaphragm 125. Line pressure from theline 44 is communicated to the chamber 108 and modulated by land 114 toenter line 58 in response to engine vacuum *which enters the chamber 126via the inlet fitting 123. Chambers 106 and 112 communicate with exhaustlines 88 and 80, respectively. The chamber 121 is vented to atmospherethrough an opening 129.

STROKE CYLINDERS The forward and reverse stroke cylinders 18 and 20include respective housings 130a and 130b having respective pistons 131and 132 slidably mounted in respective bores or central chambers 133 and134. The pistons 131 and 132 extend through openings 136 and 138 formedin the inner ends of the forward and reverse stroke cylinders 18 and 20,respectively. Springs 140 and 142 urge the respective pistons 131 and132 out through the respective openings 136 and 138 and into contactwith opposite sides of a pin or roller 144 mounted on one end of a lever146 which is pivotally mounted at its other end on a pivot pin 148. Anarm 150 is mounted at one end thereof for rotation with the lever 146and is operatively connected at its other end to the pump 12. The driveratio position, both for forward and reverse operation, is determined bythe respective axial movements of the forward and reverse pistons 131and 132, respectively. Lines 48 and 50 communicate respectively with thecentral chambers 133 and 134.

SERVO CONTROL VALVE The servo control valve 22 includes a housing 152having a central bore 154 formed therein in which a valve sleeve 155 isslidably mounted intermediate end chambers 156 and 157. The sleeve 155includes a central passage 158, annular grooves 159, 160, and 161,radial ports 162 from the passage 158 to the groove 159, adjacent radialports 163 and 164 from the passage 158 to the groove 160, and radialports 165 from the passage 158 to the groove 161. A servo valve 166 isslidably mounted in the central passage 158 of the sleeve 155. Anannular groove 167 is formed on the servo valve 166, providing regulatedpressure from the line 40 for either forward or reverse operationdepending upon the axial'position of the valve 166 with respect to therespective radial ports 162 and 165 and the forward and reversefeedlines 48 and 50. A stem 168 extends from the valve 166 through anopening 169 7 formed in an end of the housing 152. A lever 170 ispivotally mounted at one end thereof on a pivot pin 171 and is rotatedabout the pin 171 in response to rotary movement of the lever 146 viathe arm 150 and an interconnected arm 172. A pin or roller 173 is formedon the free end of the lever 170 so as to contact the end face 174 ofthe stem 168. The servo control valve 22 further includes an axialpassage 175 formed in the valve 166. Radial ports 176 communicatebetween the axial passage 175 and the chamber formed by the annulargroove 167. A retracting pin 178 is slidably mounted in the axialpassage 175 and is contacted at its outer end by a servo valve stop pin180 which is slidably mounted through spool members 182 and 184, the

latter being urged apart by a spring 186. Retainer rings 188 and 190 aremounted at predetermined points on the pin 180 adjacent the outer endsof the respective spool members 182 and 184. The end of the stop pin 180which extends away from the pin 178 is slidably mounted in an end plug192 secured to the housing 152. A threaded end portion 194 is formed onthe stop pin 180 and threadedly mounted in the end plug 192 foradjustment purposes.

MANUAL VALVE The manual valve 24 includes a housing 196 having a centralbore 198 formed therein, there being a plug 200 closing one end of thebore 198, with a selector valve stem 202 extending into the other end ofthe housing 196. A manual lever 204 is secured at the outer end of thevalve stem 202. REVERSE (63 R), NEU- TRAL (N), DRIVE (D), INTERMEDIATE(S), and LOW (L) drive ratio indicia are formed adjacent the exposedportion of the valve stem 202, the manual lever 204 being selectivelyaligned therewith. Five (5) retention balls 206, 208, 210, 212, and 214are respectively urged by springs 207, 209, 211, 213, and 215 into agroove 216 formed on the valve stem 202, depending upon the drive ratioposition of the selector lever 204. A pair of lands 218 and 220 formedon the valve stem 202 divide the bore 198 into chambers 221, 222, and223, and serve to direct ratio pressure from the line 64 into either theforward or reverse lines 94 and 96, respectively, depending upon theaxial position of the lands 218 and 220.

RATIO DISCRIMINATOR CHECK VALVE The ratio discriminator check valve 32includes a housing 294 having, a central passage 296 formed thereinincluding opposite end chambers 298 and 300. The ratio limit andconstant speed lines 66 and 62, respectively, communicate withrespective chambers 298 and 300. A two-piece sleeve member 301 and 302is secured at an intermediate location in central passage 296. An axialpassage 304 is formed through the sleeve member 301. The axial passage303 i's'enlarged at an intermediate chamber portion 306 thereof to formoppositely disposed valve Seats 308 and 310 with respect to axialpassages 303 and 304. A ball valve 312 is mounted in the portion 306 foralternate cooperation with the valve seats 308 and 310. Radial passages314 are formed in the sleeve member 302 to provide communication betweenthe chamber 306 and the line 64 leading to the manual valve assembly 24.

CONSTANT SPEED VALVE The constant speed valve 30 includes a housing 270having a bore 272 formed therein and divided into chambers 274, 276,278, and 280 by lands 282, 284, and 286 formed on a valve member 288which is slidably mounted in the bore 272. A spring 290 is mounted inthe chamber 274 between the end wall 292 of the housing 270 and theadjacent face of the land 282. Line pressure entering the chamber 276from the line 44 is modulated past the land 282 into the line 62 inresponse to the combined effect on the valve 288 of governor pressureentering the chamber 280 from the line 54 and of modulated pressureentering the chamber 278 from the vacuum modulator 16 via the line 58,against the force of the spring 290. The resultant constant speedpressure in the line 62 indicative of speed and vacuum conditionsindicative of particular throttle openings.

GOVERNOR CUT-OFF VALVE The governor cut-off valve 28 includes a housing250 having a central bore 252 formed therein in which is mounted a valve254 having lands 256 and 258 formed therein. A spring 260 is mounted ina chamber 262 of the bore 252 between an end wall 264 of the housing 250and the adjacent face of the land 256. The exhaust line 72 communicateswith the chamber 262. A chamber 266 is formed in the bore 252 betweenthe lands 256 and 258, while an end chamber 268 is formed adjacent theouter surface of the land 258. Governed pressure is communicated to theend chamber 268 via the RATIO LIMIT VALVE The ratio limit valve 26includes a housing 224 having a central bore 225 formed therein. Aregulating spool valve 226, having lands 228, 230,232, and 234 formedthereon, is slidably mounted in the bore 225, dividing the latter intochambers 236, 238, 240, 242, and 244. The chamber 236 receives governorpressure from the line 52/54. The chamber 238 is exhausted via the line74. The chamber 240 receives limit feed pressure from the line 70 andregulates same past the land 232 into the ratio limit line 66 inresponse to the effect of the governor pressure in the chamber 236 onthe regulating valve 226 within a predetermined engine speed range, say,2,400 to 4,000 rpm, as will be explained. The chamber 242 is exhaustedvia the line 76, and the chamber 244 is subjected to the regulatedpressure from the line 66 via the branchline 68 for balancing the valve226.

LOW AND INTERMEDIATE RELIEF VALVES The low and intermediate reliefvalves 34 and 36 include a housing3l6 having respective passages 318 and320'formed therein'communicating with the lines 98 and 100,respectively. Valve seats 322 and 324 are formed in the passages 318 and320, respectively, with respective suitable ball valves 326 and 328mounted adjacent thereto in chambers. 330 and 332, respectively, andurged toward the seats 322 and 324' by springs 334 and 336,respectively. Exhaust ports 338 and 340 serve to exhaust the chambers330 and 332, respectively, when therespective ball valves 326 and 328are unseated.

OPERATION It may be noted by referring to FIG. 1 that if the manualselector lever 204 is positioned in NEUTRAL (N ratio pressure enteringthe central chamber 222 of the housing 196 intermediate the lands 218and 220 will be blocked by said lands from communicating with I eitherthe reverse or forward feedlines 96 and 94, re-

spectively, the chambers 221 and 223 being open to the exhaust lines 82and 84, respectively. Hence, the spring 186 of the servo control valveassembly 22 will have returned the valve sleeve 155 to its neutralposition by having urged the spool members 182 and 184 against therespective retainer rings 188 and 190, and the infinitely variable ratiodevice 12 is not actuated. The ports communicating with the exhaustlines 78 and serve to exhaust any leakage past the respective forwardand reverse end portions of the servo control valve sleeve 155 back tothe sump 92.

Assume now that the operator has placed the selector lever 204 in theREVERSE (R) position shown in the Figure, where it is retained by virtueof the ball 206 being urged into the annular slots or grooves 216 by thespring 207. The resultant leftward movement of the land 218 of the valve202 from the abovementioned NEUTRAL position causes the fluid displacedfrom the bore 198 to the left of the land 218 to exhaust via the line82. Ratio pressure entering the bore 198 from the line 64 iscommunicated to the reverse cylinder line 96 and thence to the chamber157 of the servo control housing 152, moving the sleeve 155 to the left,against the force of the spring 186, as shown in the Figure. Thispermits line pressure from the line 40, the annular chamber 160, theradial ports 164, and the annular chamber 167 to be communicated pastthe right-hand .edge of the annular groove 167, through the radial ports165, the annular chamber 161, and the line 50 to the chamber 134 .of thestroke cylinder 20, to move the piston 132 to the left, pivotting thelever 146 to set the desired ratio position for the device 12. As thenew ratio position is being thus established, movement of the arm 150 isfed back to the arm 172, thereby pivotting the lever 170 and rollerl73to cause the stem 168 and, hence, the valve 166.to assume a balancedregulating position with the annular groove 167 being centered betweenthe radial ports 162 and 165, until such time as signals indicative ofengine speed and/or engine vacuum change, as will be explained.

Next, consider the placing of the manual lever 204 in DRIVE (D")position, the springloaded ball 210 in the annular notch 216 serving toretain the valvest'em 202 in such position. The resultant position ofthelands 218 and 220 is such that ratio limit pressure from the line 64 isdirected via the chamber 222 to the line 94 and, thence, to the chamber156 of the servo control valve 22 to move the sleeve to the rightagainst the force'of the spring 186, the spool member 184 being abuttedagainst the retainer ring 190, to thus cause line pressure from the line40 to be communicated via the annular groove 160, the ports 163, pastthe left-hand edge of the annular groove 167, to the ports 162 and theannular groove 159, thence to the forward feedline 48 to position thepiston 131,'the roller 144, the lever 146, and the arm 150 accordingly.This establishes the ratio pressure for the continuously variable device12. Feedback through the arm 172, the lever 170, the roller 173, thestem 168, and the valve 166 positions the latter in a balancedregulating position, with the annular groove 167 thereof centeredbetween the radial servo control valve 22 and, thence, to the controlleddevice 12, the curve finally attained thereby being the maximum speedratio curve illustrated in FIG. 2. Typically, part-throttle accelerationoccurs at a constant or nearly constant engine speed, such as constantspeed line a (FIG. 2), depending on throttle opening, until the maximumspeed ratio curve is reached. Normally all steady-state road loadoperation will not be along the maximum speed ratio curve, comparable toa direct drive condition in a conventional geared transmission.Part-throttle acceleration, operation on grades, for example, can, ofcourse, occur at any point between the full-throttle and ratio limitcurves, for example, along constant speed line a(FlG. 2) until somespeed ratio curve c is reached.

Specifically, this is accomplished by virtue of any change in governorpressure and/or in modulated pressure, as a result of engine speedchanges from either a manually initiated change in the throttle settingor the encountering of nonlevel road conditions, being directed via thelines 52 and 58, respectively, to the respective chambers 280 and 278 ofthe constant speed valve assembly 30. The resultant combined effect onthe faces of the lands 286 and 284, respectively, as opposed by theforce of the-spring 290, moves the valve 288 so as to modulate the linepressure communicated to the chamber 276 from the mainline 42/44 pastthe adjacent edge of the land 282 and into the line 62. Such modifiedconstant speed pressure is thereupon communicated to the chambers 300and 306 of the ratio discriminator check valve assembly 32 and, thence,via the ports 314, the line 64, the chamber 222 of the manual valveassembly 24, and the line 94 to the servo control valve assembly 22 forchanging the ratio position of the device 12 accordingly.

It may be noted that during part-throttle operation the pressure in thechambers 300 and 306 of the ratio discriminator check valve assembly 32is sufficient to retain the ball valve 312 on the seat 308 inasmuch asthe pressure in the chamber 298 is influenced by changes in governorpressure only via the valve assemblies 28 and 26.

Consider now a full-throttle increase in speed. The immediate result isto eliminate any modulated vacuum effect on the constant speed valvechamber 278 on the face of the land 284, permitting the spring 290 toclose off the constant speed line 62 from the main feedline 44.Concurrently, governor pressure in the lines 52, 54, and 56 isincreased, causing the governor cut-off valve 254 to move to the left,against the force of the spring 260, increasing the effect of linepressure from the line 46 on the limit feed pressure in the line 70. Thegovernor signal from the line 54 in the left end chamber 236 of theratio limit valve 226 moves the latter to the right, permitting theincreased limit feed pressure from the line 70 to be communicated pastthe land 232, to the ratio limit line 66. The valve 226 seeks a newposition, balanced by the changed governor pressure on the left endthereof and the changed ratio limit pressure on the right end thereof. II

The resultant ratio limit pressure is communicated via the line 66 tothe left end of the ratio discriminator check valve housing 294 and,hence, to the ball valve 312 which is now readily moved off the seat 308and across the chamber 306 to the seat 310.

The above-described increased ratio limit pressure in the chamber 298 isthus communicated through the radial ports 314 to the line 64, andthence to the bore 198 of the manual valve assembly 24 intermediate thelands 218 and 220 and via the line 94 to the chamber 156 of the servocontrol valve assembly 22 to thereby cause a change in the ratioposition for the device 12 along the full-throttle curve shown in FIG.2, rather than along the maximum performance line which would have beenthe full-throttle result without the influence of the valve assemblies26 and 28. The noise element of a rapid rise in engine speed along themaximum performance line would be highly objectionable.

Should the manual lever 204 be placed on INTER- MEDIATE S,33 or LOW L,it may be noted that the land 220 would be positioned to the right ofthe lines and 98, respectively, with the respective intermediate and lowrelief valves 328 and 326 limiting the pressure in the forward cylinderline 94 and, hence, in the chamber 156 of the servo control valveassembly 22 to respective predetermined lower pressures, say, 63 and 36psi, resulting in steeper linear curves to the left of the direct drivecurve of FIG. 2.

It should be apparent that the invention provides a simplified hydrauliccontrolsystem wherein an infinitely variable drive ratio is accomplishedin an efficient, smooth and acoustically acceptable manner, under bothpart-throttle and full-throttle conditions, for use with continuouslyvariable transmissions, such as a hydrostatic transmission or a toric"transmission.

It should also be apparent that a suitable spool valve arrangement couldbe utilized in lieu of the low and intermediate relief or blow-offvalves 34 and 36.

While but one embodiment ofthe invention has been shown and described,other modifications thereof are possible.

We claim:

l.-For use with an infinitely variable device, a hydraulic controlsystem comprising a source of fluid under pressure, an engine governorassembly for providing a fluid signal indicative of engine speed, avacuum modulator assembly for providing a fluid signal indicative ofengine vacuum, servo control means for selectively moving saidinfinitely variable device to establish the ratio position thereof,constant speed valve means for receiving said fluid signals indicativeof engine speed and engine vacuum from said respective engine governorand vacuum modulator assemblies and varying the pressure of said fluidunder pressure to correspond to said speed and vacuum conditions underpart-throttle conditions to provide a ratio fluid signal, valve limitingmeans for receiving said fluid signal indicative of engine speed above apredetermined engine speed under full-throttle conditions to provide afullthrottle fluid signal, and manual valve means for receiving saidratio fluid signal'under said part-throttle conditions and for receivingsaid full-throttle fluid signal under said full-throttle conditions anddirecting same to said servo control means.

2. For use with an infinitely variable device a hydraulic control systemComprising a source of fluid under pressure, an engine governor assemblyfor providing a fluid signal indicative of engine speed, a vacuummodulator assembly for providing a fluid signal indicative of enginevacuum, servo control means for selectively moving said infinitelyvariable device to establish the ratio position thereof, constant speedvalve means for receiving said fluid signals indicative of engine speedand engine vacuum from said respective engine govertrol means.

3. The hydraulic control system described in claim 2, wherein said servocontrol means includes forward and reverse feed control valve means formoving said infinitely variable device into forward or reverse operatingposition, and forward and reverse feedlines communicating said fluidsignal from said manual valve means to one of said forward and reversefeed control valve means depending upon the selected position of saidmanual valve means.

4. The hydraulic control system described in claim 2, and low andintermediate relief valves operatively connected to said manual valvemeans to limit the pressure of the fluid signal being directed by saidmanual valve means to said servo control means upon the selective manualpositioning of said manual valve means.

5. For use with an infinitely variable device, a hydraulic controlsystem comprising a source of fluid under pressure, an engine governorassembly for providing a fluid signal indicative of engine speed, avacuum modulator assembly for providing a fluid signal indicative ofengine vacuum, servo control means for selectively moving saidinfinitely variable device into forward or reverse operating positionand establishing the ratio position thereof, constant speed valve meansfor receiving said fluid signals indicative of engine speed and enginevacuum from said respective engine governor and vacuum modulatorassemblies and varying the pressure of said fluid under pressure tocorrespond to said speed and vacuum conditions to provide maximum speedratio operation, valve limiting means for receiving said fluid signalindicative of engine speed and varying the pressure of said fluid underpressure to provide aregulated fluid pressure signal for overruling saidconstant speed valve means above a predetermined engine 'speed underfull-throttle conditions to provide fullthrottle curve operation, checkvalve means for receiving said varied pressure signal from said constantspeed valve means and said regulated fluid pressure signal from saidvalve limiting means and permitting only the higher pressure one of saidtwo signals to pass therethrough, and manual valve means for receivingone of said varied pressure signals and said regulated fluid pressuresignal from said check valve means and selectively directing same viaforward or reverse feedlines to said servo control means.

6. For use with an infinitely variable device, a hydraulic controlsystem comprising a source of fluid under pressure, an engine governorassembly for providing a fluid signal indicative of engine speed, avaclid uum modulator assembly for providing a fluid signal indicative ofengine vacuum, servo control means for selectively moving saidinfinitely variable device into forward or reverse operating positionand establishing the ratio position thereof, constant speed valve meansfor receiving said fluid signals indicative of engine speed and enginevacuum from said respective engine governor and vacuum modulatorassemblies and varying the pressure of said fluid under pressure tocorrespondto said speed and vacuum conditions to provide maximum speedratio operation, valve limiting means for receiving said fluid signalindicative of engine speed and varying the pressure of said fluid underpressure to provide a regulated fluid pressure signal above apredetermined engine speed to provide full-throttle operation, ratiodiscriminator check valve means for receiving said varied pressuresignal from said constant speed valve means and said regulated fluidpressure signal from said valve limiting means and transmitting saidvaried pressure signal during part-throttle conditions and saidregulated fluid pressure signal during full-throttle conditions, andmanual valve means for receiving said transmitted varied pressure signalor regulated fluid pressure signal from said check valve means andselectively directing same via forward or reverse feedlines to saidservo control means.

7. For use with an infinitely variable device, a hydraulic controlsystem comprising a source of fluid under pressure, an engine governorassembly for providing a fluid signal indicative of engine speed, avacuum modulator assembly for providing a fluid signal in dicative ofengine vacuum, servo control means for selectively moving saidinfinitely variable device into forward or reverse operating positionand establishing the ratio position thereof, constant speed valve meansfor receiving said fluid signals indicative of engine speed and enginevacuum from said respective engine governor and vacuum modulatorassemblies and varying the pressure of said fluid under pressure tocorrespond to said speed and vacuum conditions to provide a fluid signalfor maximum speed ratio curve operation, governor cut-off valve meansfor receiving said fluid signal indicative of engine speed andresponding to said signal when said signal is indicative of a speedhigher than a predetermined engine speed and varying the pressure ofsaid fluid under pressure to provide a fluid signal correspondingthereto, ratio limit valve means for receiving both said varied pressuresignal from said governor cut-off means and said fluid signal indicativeof engine speed and providing a regulated fluid signal for full-throttlecurve operation, check valve means for receiving said varied pressuresignal from said constant speed valve means and said regulated fluidpressure signal from said ratio limit valve means and permitting onlythe higher pressure one of said two signals to pass therethrough, andmanual valve means for receiving one of said varied pressure signal andsaid regulated fluid pressure signal from said check valve means andselectively directing same via forward or reverse feedlines to saidservo control means.

1. For use with an infinitely variable device, a hydraulic controlsystem comprising a source of fluid under pressure, an engine governorassembly for providing a fluid signal indicative of engine speed, avacuum modulator assembly for providing a fluid signal indicative ofengine vacuum, servo control means for selectively moving saidinfinitely variable device to establish the ratio position thereof,constant speed valve means for receiving said fluid signals indicativeof engine speed and engine vacuum from said respective engine governorand vacuum modulator assemblies and varying the pressure of said fluidunder pressure to correspond to said speed and vacuum conditions underpart-throttle conditions to provide a ratio fluid signal, valve limitingmeans for receiving said fluid signal indicative of engine speed above apredetermined engine speed under fullthrottle conditions to provide afull-throttle fluid signal, and manual valve means for receiving saidratio fluid signal under said part-throttle conditions and for receivingsaid fullthrottle fluid signal under said full-throttle conditions anddirecting same to said servo control means.
 2. For use with aninfinitely variable device a hydraulic control system comprising asource of fluid under pressure, an engine governor assembly forproviding a fluid signal indicative of engine speed, a vacuum modulatorassembly for providing a fluid signal indicative of engine vacuum, servocontrol means for selectively moving said infinitely variable device toestablish the ratio position thereof, constant speed valve means forreceiving said fluid signals indicative of engine speed and enginevacuum from said respective engine governor and vacuum modulatorassemblies and varying the pressure of said fluid under pressure tocorrespOnd to said speed and vacuum conditions during part-throttleoperation, valve limiting means for receiving said fluid signalindicative of engine speed and providing a regulated fluid pressuresignal for overruling said constant speed valve means above apredetermined engine speed during full-throttle operation, and manualvalve means for receiving said varied pressure signal during saidpart-throttle operation and for receiving said regulated fluid pressuresignal during said full-throttle operation and selectively directingsame to said servo control means.
 3. The hydraulic control systemdescribed in claim 2, wherein said servo control means includes forwardand reverse feed control valve means for moving said infinitely variabledevice into forward or reverse operating position, and forward andreverse feedlines communicating said fluid signal from said manual valvemeans to one of said forward and reverse feed control valve meansdepending upon the selected position of said manual valve means.
 4. Thehydraulic control system described in claim 2, and low and intermediaterelief valves operatively connected to said manual valve means to limitthe pressure of the fluid signal being directed by said manual valvemeans to said servo control means upon the selective manual positioningof said manual valve means.
 5. For use with an infinitely variabledevice, a hydraulic control system comprising a source of fluid underpressure, an engine governor assembly for providing a fluid signalindicative of engine speed, a vacuum modulator assembly for providing afluid signal indicative of engine vacuum, servo control means forselectively moving said infinitely variable device into forward orreverse operating position and establishing the ratio position thereof,constant speed valve means for receiving said fluid signals indicativeof engine speed and engine vacuum from said respective engine governorand vacuum modulator assemblies and varying the pressure of said fluidunder pressure to correspond to said speed and vacuum conditions toprovide maximum speed ratio operation, valve limiting means forreceiving said fluid signal indicative of engine speed and varying thepressure of said fluid under pressure to provide a regulated fluidpressure signal for overruling said constant speed valve means above apredetermined engine speed under full-throttle conditions to providefull-throttle curve operation, check valve means for receiving saidvaried pressure signal from said constant speed valve means and saidregulated fluid pressure signal from said valve limiting means andpermitting only the higher pressure one of said two signals to passtherethrough, and manual valve means for receiving one of said variedpressure signals and said regulated fluid pressure signal from saidcheck valve means and selectively directing same via forward or reversefeedlines to said servo control means.
 6. For use with an infinitelyvariable device, a hydraulic control system comprising a source of fluidunder pressure, an engine governor assembly for providing a fluid signalindicative of engine speed, a vacuum modulator assembly for providing afluid signal indicative of engine vacuum, servo control means forselectively moving said infinitely variable device into forward orreverse operating position and establishing the ratio position thereof,constant speed valve means for receiving said fluid signals indicativeof engine speed and engine vacuum from said respective engine governorand vacuum modulator assemblies and varying the pressure of said fluidunder pressure to correspond to said speed and vacuum conditions toprovide maximum speed ratio operation, valve limiting means forreceiving said fluid signal indicative of engine speed and varying thepressure of said fluid under pressure to provide a regulated fluidpressure signal above a predetermined engine speed to providefull-throttle operation, ratio discriminator check valve means forreceiving said varied pressure signal froM said constant speed valvemeans and said regulated fluid pressure signal from said valve limitingmeans and transmitting said varied pressure signal during part-throttleconditions and said regulated fluid pressure signal during full-throttleconditions, and manual valve means for receiving said transmitted variedpressure signal or regulated fluid pressure signal from said check valvemeans and selectively directing same via forward or reverse feedlines tosaid servo control means.
 7. For use with an infinitely variable device,a hydraulic control system comprising a source of fluid under pressure,an engine governor assembly for providing a fluid signal indicative ofengine speed, a vacuum modulator assembly for providing a fluid signalindicative of engine vacuum, servo control means for selectively movingsaid infinitely variable device into forward or reverse operatingposition and establishing the ratio position thereof, constant speedvalve means for receiving said fluid signals indicative of engine speedand engine vacuum from said respective engine governor and vacuummodulator assemblies and varying the pressure of said fluid underpressure to correspond to said speed and vacuum conditions to provide afluid signal for maximum speed ratio curve operation, governor cut-offvalve means for receiving said fluid signal indicative of engine speedand responding to said signal when said signal is indicative of a speedhigher than a predetermined engine speed and varying the pressure ofsaid fluid under pressure to provide a fluid signal correspondingthereto, ratio limit valve means for receiving both said varied pressuresignal from said governor cut-off means and said fluid signal indicativeof engine speed and providing a regulated fluid signal for full-throttlecurve operation, check valve means for receiving said varied pressuresignal from said constant speed valve means and said regulated fluidpressure signal from said ratio limit valve means and permitting onlythe higher pressure one of said two signals to pass therethrough, andmanual valve means for receiving one of said varied pressure signal andsaid regulated fluid pressure signal from said check valve means andselectively directing same via forward or reverse feedlines to saidservo control means.